Research In Motion fell after replacing co-CEOs Jim Balsillie and Mike Lazaridis with an insider who said he sees no need for radical change as the company struggles to compete with Apple.

Thorsten Heins, a chief operating officer who joined RIM four years ago from Siemens, will replace the pair in the CEO post effective immediately, RIM said in a statement. Director Barbara Stymiest will take over as chairman, as the two also cede their co-chairmen positions. Lazaridis, who founded RIM in 1984, will become vice chairman; Balsillie will remain a board member without any operational role.

Balsillie and Lazaridis showed little sign of being able to stop Apple and Google’s gains as the Silicon Valley companies remade the mobile-computing market with devices such as the iPhone and iPad. Waterloo, Ontario-based RIM’s stock tumbled 75 percent last year as sales slumped, and the two men, both 50, drew investor criticism for releasing products without the features necessary to compete.

RIM fell 8.5 percent to $15.56 at the close, the biggest drop in a month, after Heins told investors on a conference call that no “drastic change” is needed. Shares had rallied as much as 7.6 percent before the call.

RIM, once the most valuable company in Canada, has lost 89 percent since its peak in 2008, when soaring BlackBerry sales pushed its market value to more than $80 billion. Last quarter, sales fell about 6 percent to $5.17 billion.

Lazaridis, Balsillie and Stymiest all said the decision to step down was their own and not a response to outside pressure.